This invention relates to an interventional catheter comprising a catheter tube having two superposed layers of materials secured together and with mechanical properties differing from one another, a guidewire lumen in the catheter tube for the sliding fit of a guidewire, and a balloon with a distal end sealingly surrounding the catheter tube whereby the catheter tube has an inner layer forming the guidewire lumen and an outer layer forming an outer surface of the catheter tube.
Over the wire catheters have been widely used for interventions such as percutaneous transluminal cardiovascular angioplasty. A problem with these catheters is that the guidewire may clog into the guidewire lumen of the catheter, whereby the guidewire may follow the balloon upon withdrawal thereof after the inflation procedure thereby making it necessary to re-insert the guidewire into the treated area of the blood vessel for repositioning a balloon therein in case a second inflation is needed. A further problem is that the catheter has to achieve an acceptable compromise between the requirements of some stiffness to assure good pushability and some flexibility to assure kink resistance. In addition, the catheter has to permit safe attachment of the balloon to the catheter tube.
Monorail.RTM. technology, which provides for an entry of the guidewire distal of the balloon and an exit for the guidewire distal of the proximal end of the catheter tube, substantially reduces the risk of the guidewire clogging in the guidewire lumen because the length of frictional engagement between the guidewire and the guidewire lumen is strongly reduced. That is also of great help in the handling of balloon catheters for balloon exchange purposes. Though limited, the friction and clogging problem is, however, still existent.
Two layer catheter shafts have been developed. For example, the document WO 92/11893 describes an intra-aortic balloon apparatus comprising a hollow catheter in which is located an elongated member forming a central lumen extending out of the catheter at the distal end thereof. An aortic pumping balloon is positioned over the elongated member; the distal end of the balloon is bonded to a tip affixed to the distal end of the elongated member, and its proximal end is bonded to the distal end of the catheter. In order to achieve a balance of flexibility and remains and to avoid kinking, the elongated member is formed of an inner layer comprised of a soft elastomeric material to impart flexibility to the tubing and the outer layer is comprised of a hard plastic material to impart structural support to the elongated member. This balloon apparatus cannot be loaded with a guidewire and moved into tortuous vessels with the guidewire loaded inside the elongated member as the friction between guidewire and elongated member increases distinctively when the elongated member is shaped into curves. There would be therefore the risk that a spiral wound guidewire could be captured in the soft elastomeric plastic material of the inner layer of the elongated member. Although the outer layer of the elongated member that is coextruded onto the inner layer is formed of nylon, a material which is expected to be directly weldable to a wide variety of materials, this balloon apparatus cannot be introduced into narrow vessels or narrow stenoses, nor can it be passed through narrow punctures to enter the blood vessels. This is because of the relatively large profile of the folded balloon, due to the distal fixture of the balloon to the elongated member. The balloon is bonded to an intermediate tip element which in turn is bonded to the elongated member.
The document EP 0 650 740 A1 shows a catheter comprising a catheter tube having two superposed layers of materials secured in relation to one another and with mechanical properties differing from one another, a longitudinal lumen in the catheter tube for the sliding fit of a guidewire, and a balloon with a proximal end and a distal end, the distal end sealingly surrounding the catheter tube, whereby the catheter tube has an inner layer forming the longitudinal lumen and an outer layer forming the outer surface of the catheter tube. In this catheter, the inner layer is formed of a material with lower friction coefficient than the material forming the outer layer, whereby there is no more risk of having the guidewire clogging in the guidewire lumen of the catheter tube.
In terms of two layers catheter shafts, it has been observed that in practical use the adhesion of the two layers of material was not absolutely satisfactory. Although the coextrusion technology currently used for making such catheter shafts seems to involve close molecular interpenetration of the materials forming the superposed layers of the shaft, it has been possible to observe separation of the two layers, for example at the place of insertion of the shaft over the guidewire. Furthermore, tear test effected on such structures has shown that the two layers can separate under extreme conditions of stress on the shaft.
It is an object of this invention to propose an interventional balloon catheter avoiding the aforesaid drawbacks. A further object of the invention is an interventional catheter structure which is versatile and which provides a fully controllable and easy to manufacture assembly. Still a further object of the invention is an interventional low profile balloon catheter that can be safely operated on a guidewire and moved into tortuous vessels and other extreme conditions.
Various multilayer catheters are known in the art. Reference is made to U.S. Pat. Nos. 4,627,844; 4,636,346; 5,403,292; 5,499,973; and 5,538,510.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.